Aldosterone is a steroid hormone secreted in the adrenal cortex. In primary cells of the distal tubules and collecting ducts of the kidney, aldosterone binding to the mineralocorticoid receptor (MR) results in the retention of sodium and water and excretion of potassium, which in turn leads to increased blood pressure. Aldosterone also causes inflammation that leads to fibrosis and remodeling in the heart, vasculature and kidney. This inflammation may proceed by MR-dependent as well as MR-independent mechanisms (Gilbert, K. C. et al., Curr. Opin. Endocrinol. Diabetes Obes., vol. 17, 2010, pp. 199-204).
Mineralocorticoid receptor antagonists (MRAs) such as spironolactone and eplerenone have been used previously to block the effects of aldosterone binding to MR. When given in addition to standard therapies such as angiotensin-converting enzyme (ACE) inhibitors and loop diuretics, the nonselective MRA spironolactone and the selective MRA eplerenone significantly reduced morbidity and mortality in patients with heart failure or myocardial infarction (Pitt, B. et al., New Engl. J. Med., vol. 341, 1999, pp. 709-717; Pitt, B. et al., New Engl. J. Med., vol. 348, 2003, pp. 1382-1390). However, the nonselective MRA spironolactone can also bind to and act at other steroid receptors, and as a consequence its use is associated with sexual side effects such as gynecomastia, dysmenorrhoea and impotence (Pitt, B. et al., New Engl. J. Med., vol. 341, 1999, pp. 709-717; MacFadyen, R. J. et al., Cardiovasc. Res., vol. 35, 1997, pp 30-34; Soberman, J. E. et al., Curr. Hypertens. Rep., vol. 2, 2000, pp 451-456). Additionally, both spironolactone and eplerenone are known to cause elevated plasma potassium levels (hyperkalemia) and elevated aldosterone levels.
An alternative method of blocking the effects of aldosterone is to inhibit its biosynthesis. CYP11B2 (aldosterone synthase) is a mitochondrial cytochrome P450 enzyme that catalyzes the final oxidative steps in the conversion of 11-deoxycorticosterone, a steroidal precursor, to aldosterone (Kawamoto, T. et al., Proc. Natl. Acad. Sci. USA, vol. 89, 1992, pp. 1458-1462). Compounds that inhibit CYP11B2 should thus inhibit the formation of aldosterone. Such compounds, particularly those of nonsteroidal structure, should provide the beneficial effects of MRAs, without the adverse effects derived from steroid receptor binding or MR-independent inflammatory pathways.
CYP11B1 (steroid-11β-hydroxylase) is a related enzyme that catalyzes the formation of glucocorticoids such as cortisol, an important regulator of glucose metabolism. Because human CYP11B2 and CYP11B1 are greater than 93% homologous, it is possible for nonselective compounds to inhibit both enzymes (Kawamoto, T. et al., Proc. Natl. Acad. Sci. USA, vol. 89, 1992, pp 1458-1462; Taymans, S. E. et al., J. Clin. Endocrinol. Metab., vol. 83, 1998, pp 1033-1036). It would be preferable, however, for therapeutic agents to selectively inhibit CYP11B2 and the formation of aldosterone with diminished inhibition of, or affect on, CYP11B1 and the production of cortisol. The compounds of the invention provide an alternative to previous treatments for elevated aldosterone levels and selectively inhibit CYP11B2 as compared to CYP11B1.